Genmab A/S has announced additional data from the interim analysis of the ofatumumab (Arzerra™) Phase III study, PROLONG (OMB112517). The study evaluated ofatumumabmaintenance therapy versus no further treatment (observation) in patients with a complete response (CR) or partial response (PR) after 2nd or 3rd line treatment for chronic lymphocytic leukemia (CLL). The improvement in the study’s primary endpoint, progression free survival (PFS), met the prespecified statistical significance level for the interim analysis.

A total of 474 patients were included in the interim analysis. Patients who received ofatumumab maintenance treatment lived 13.4 months longer without their disease worsening (median PFS) than patients who received no further treatment. Median PFS was 28.6 months for the ofatumumab treatment arm and 15.2 months for the observation arm (Hazard Ratio 0.48; p<0.0001).

The amount of time until patients started their next therapy was significantly longer in the ofatumumab treatment arm than in the observation arm (median 38.0 months vs 27.4 months, Hazard Ratio 0.63; p=0.0076).

There were no unexpected safety findings. Adverse events occurred in 87% of patients in the ofatumumab treatment arm versus 75% in the observation treatment arm. In the ofatumumab treatment arm, 25% of patients experienced grade 3-4 adverse events compared to 17% in the observation arm. Grade 3-4 infections were 18% in the ofatumumab arm and 13% in the observation arm. The two most common grade 3-4 adverse events were neutropenia (22% in ofatumumab arm vs 9% in observation arm), and pneumonia (7% in ofatumumab arm vs 4% in observation arm). The death rate was similar in both arms (14%).

“The interim results of this study show that ofatumumab maintenance therapy significantly extended the amount of time the patients in the study lived without their CLL symptoms getting worse,” said Jan van de Winkel, Ph.D., Chief Executive Officer of Genmab.

These data will be presented in an oral session at the 56th Annual Meeting of the American Society of Hematology (ASH) in San Francisco, California on December 6.

About PROLONG
This Phase III study was designed to randomize up to 532 patients with relapsed CLL who have responded to treatment at relapse, to either ofatumumab maintenance treatment or no further treatment (observation). The study is no longer recruiting patients. Patients in the ofatumumab arm received an initial dose of 300 mg of ofatumumab, followed one week later by a second dose of 1,000 mg, then doses of 1,000 mg every 8 weeks for up to two years, while patients in the observation treatment arm received no further treatment.

The primary endpoint of the study is PFS. Secondary objectives will evaluate clinical benefit, overall survival, safety, tolerability, the health-related quality of life of subjects treated with ofatumumab versus no further treatment, and pharmacokinetics among relapsed CLL patients receiving maintenance therapy with ofatumumab.